1. Field of the Invention
This invention relates to agricultural machinery having resiliently mounted attachments.
The invention is particularly useful when applied to forage harvesters having attachments, such as a pick-up means which, in operation, should closely follow the ground contours. While the invention will be described hereafter in further detail in connection with a pick-up mechanism for a forage harvester, the invention is equally well applied to other agricultural machinery having other attachments such as, for example, a direct-cut attachment for forage harvesters and a header for mower-conditioners. The terms "forward" and "rearward" used throughout the specification are with respect to the direction of movement of the machine in operation.
2. Description of the prior art
Known forage harvesters normally have a wheel-supported framework upon which the cutterhead is mounted. Since crop lying on the ground has to be lifted therefrom and fed to the cutterhead by the pick-up mechanism, it is clear that in operation the pick-up mechanism should closely follow the contours of the ground so as to operate properly. Therefore, in known forage harvesters, the pick-up mechanism is pivotally mounted in front of the cutterhead in a crop transfer relationship. The pivot axis of the pick-up mechanism is provided at the rearward side thereof.
Some known forage harvesters further comprise a pick-up lifting mechanism having a pair of forwardly-extending arms and another upwardly-extending arm. This lifting mechanism is pivotally mounted on the framework at a location substantially below the pick-up pivot axis and is arranged so that the pair of forwardly-extending arms project below the pick-up mechanism to support and lift the latter. The upwardly-extending arm is positioned rearwardly of the pick-up pivot axis. Tension spring means may extend between the upper end of the upwardly-extending arm and a portion of the framework and be arranged to compensate the major part of the weight torque of the pick-up means tending to pivot the pick-up means downwardly. Thus, when in operation the pick-up mechanism just contacts the ground and as ground irregularities are encountered, the pick-up mechanism is more or less caused to float over these.
While in general the above described known arrangement has heretofore been satisfactory, this structure still has some disadvantages which become more significant when the same principles are applied to a selfpropelled harvester.
Indeed, assuming that with the above described known forage harvester the pick-up is momentarily positioned above a dip in the ground, then theoretically the pick-up mechanism should automatically be pivoted downwardly. Thereby the centre of gravity of the pick-up mechanism would move to a position which, when seen in fore-and-aft direction, is closer to the pivot axis of the pick-up mechanism. This means that the weight torque around the pivot axis decreases. Theoretically, the compensation torque should be decreased accordingly. However, as the aforementioned tension spring is stretched by a downward movement of the pick-up mechanism and as the perpendicular distance between the pivot axis of the pick-up lifting mechanism and the spring is also slightly increased, the compensation torque is increased, rather than decreased, by a downward movement of the pick-up mechanism. This will, of course, result in the pick-up mechanism not properly following the contours of the ground surface, i.e. the known compensation mechanism does not operate satisfactorily.
On pull-type forage harvesters, the pick-up mechanism is installed close to the supporting wheels. As a result, provided the ground irregularities are not too sharp, the whole machine can more or less follow the ground contour, whereby the compensating mechanism of the pick-up means should only have angularly to adjust the position of the pick-up means over a relatively small range.
On a self-propelled forage harvester, the pick-up mechanism is installed normally much further in front of the front wheels. This necessitates the pick-up mechanism being angularly adjustable over a much larger range. This is aggravated by the rear wheels of the self-propelled forage harvesters being positioned even further rearwardly. Indeed, when these wheels momentarily enter a dip while the front wheels ride over a bump, the whole machine is pivoted around the front wheel axis, whereby the pick-up mechanism, which is positioned in front of this wheel axis, has to be pivoted in an opposite direction over a still larger angle. It will, therefore, be clear that the disadvantage which is inherent to the known structure, is aggravated when the same structure is embodied on a self-propelled machine.
Furthermore, some known forage harvesters also comprise a hydraulic lifting cylinder which acts directly on the upwardly-extending arm of the lifting mechanism so that, when desired, it can override the compensation mechanism and pivot the pick-up mechanism from the operative position to a raised transport position. However, when the pick-up is in the operative position, this hydraulic cylinder sometimes may adversely affect the operation of the compensation mechanism.
Also, in the known arrangement, a relatively large number of components have to move during the compensation operation. This results in considerable frictional forces between the various components as well as inertia forces which all adversely influence the proper compensation operation.